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Rapid recognition of Japanese sake quality (flavor and types of sake) is an important factor affecting consumers’ preference, quality control, as well as fraud avoidance in sake labelling. This stu...

NAD(P) + -dependent aldehyde dehydrogenase (EC 1.2.1.5) and aspartase (EC 4.3.1.1) in the cells of an atypical psychrophile from Antarctic seawater, Cytophaga sp. KUC-1, were paradoxically thermostable, although they derived from a psychrophile. Both enzymes showed the highest activity at about 55 °C, and also active even under cold conditions. The enzymes contained more Ile residues than the enzymes from mesophiles. The Ile/Ile + Val + Leu ratio of the Cytophaga thermostable enzymes was much higher than that of the enzymes from mesophiles. As compared with the enzymes from other microorganisms, the Cytophaga thermostable enzymes have the structural differences in the C-terminal region of the enzymes. Therefore, the C-terminal region might be important for the paradoxical thermostability of the enzymes. The psychrophilic microorganism produces not only psychrophilic enzyme, but thermostable enzyme with psychrophilicity. Therefore, the psychrophilic microorganism is one of the candidates for isolation of novel biocatalysts, which have potential for various industrial applications.

D-Arginase activity was found in the cells of an isolate, Arthrobacter sp. KUJ 8602, grown in the L-arginine medium, and the enzyme was purified and characterized. Its molecular weight was estimated to be about 232,000 by gel filtration, and that of the subunit was approximately 40,000 by SDS-PAGE, suggesting that the enzyme is a homohexamer. The enzyme acted on not only D-arginine but also 4-guanidinobutyrate, 3-guanidinopropionate and even L-arginine. The V(max)/K(m) values for 4-guanidinobutyrate and D-arginine were determined to be 87 and 0.81 micro mol/min/mg/mM, respectively. Accordingly, the enzyme is regarded as a kind of guanidinobutyrase [EC 3.5.3.7]. The pH optima for 4-guanidinobutyrate and D-arginine were 9.0 and 9.5, respectively. The enzyme was inhibited competitively by 5-aminovalerate, and thiol carboxylates such as mercaptoacetate served as strong mixed-type inhibitors. The enzyme contained about 1 g-atom of firmly bound Zn(2+) per mol of subunit, and removal of the metal ions by incubation with 1,10-phenanthroline resulted in loss of activity. The inactivated enzyme was reactivated markedly by incubation with either Zn(2+) or Co(2+), and slightly by incubation with Mn(2+). The nucleotide sequence of enzyme contains an open reading frame that encodes a polypeptide of 353 amino acid residues (M(r): 37,933). The predicted amino acid sequence contains sequences involved in the binding of metal ions and the guanidino group of the substrate, which show a high homology with corresponding sequences of Mn(2+)-dependent amidinohydrolases such as agmatinase from Escherichia coli and L-arginase from rat liver, though the homology of their entire sequences is relatively low (24-43%).

An NAD(+)-dependent alcohol dehydrogenase of a psychrotorelant from Antarctic seawater, Flavobacterium frigidimaris KUC-1 was purified to homogeneity with an overall yield of about 20% and characterized enzymologically. The enzyme has an apparent molecular weight of 160k and consists of four identical subunits with a molecular weight of 40k. The pI value of the enzyme and its optimum pH for the oxidation reaction were determined to be 6.7 and 7.0, respectively. The enzyme contains 2 gram-atoms Zn per subunit. The enzyme exclusively requires NAD(+) as a coenzyme and shows the pro-R stereospecificity for hydrogen transfer at the C4 position of the nicotinamide moiety of NAD(+). F. frigidimaris KUC-1 alcohol dehydrogenase shows as high thermal stability as the enzymes from thermophilic microorganisms. The enzyme is active at 0 to over 85 degrees C and the most active at 70 degrees C. The half-life time and k (cat) value at 60 degrees C were calculated to be 50 min and 27,400 min(-1), respectively. The enzyme also shows high catalytic efficiency at low temperatures (0-20 degrees C) (k(cat)/K(m) at 10 degrees C; 12,600 mM(-1)min(-1)) similar to other cold-active enzymes from psychrophiles. The alcohol dehydrogenase gene is composed of 1,035 bp and codes 344 amino acid residues with an estimated molecular weight of 36,823. The sequence identities were found with the amino acid sequences of alcohol dehydrogenases from Moraxella sp. TAE123 (67%), Pseudomonas aeruginosa (65%) and Geobacillus stearothermophilus LLD-R (56%). This is the first example of a cold-active and thermostable alcohol dehydrogenase.

We found that a psychrophilic bacterium isolated from Antarctic seawater, Cytophaga sp. KUC-1, abundantly produces aspartase [EC4.3.1.1], and the enzyme was purified to homogeneity. The molecular weight of the enzyme was estimated to be 192,000, and that of the subunit was determined to be 51,000: the enzyme is a homotetramer. L-Aspartate was the exclusive substrate. The optimum pH in the absence and presence of magnesium ions was determined to be pH 7.5 and 8.5, respectively. The enzyme was activated cooperatively by the presence of L-aspartate and by magnesium ions at neutral and alkaline pHs. In the deamination reaction, the K(m) value for L-aspartate was 1.09 mM at pH 7.0, and the S(1/2) value was 2.13 mM at pH 8.5. The V(max) value were 99.2 U/mg at pH 7.0 and 326 U/mg at pH 8.5. In the amination reaction, the K(m) values for fumarate and ammonium were 0.797 and 25.2 mM, respectively, and V(max) was 604 U/mg. The optimum temperature of the enzyme was 55 degrees C. The enzyme showed higher pH and thermal stabilities than that from mesophile: the enzyme was stable in the pH range of 4.5-10.5, and about 80% of its activity remained after incubation at 50 degrees C for 60 min. The gene encoding the enzyme was cloned into Escherichia coli, and its nucleotides were sequenced. The gene consisted of an open reading frame of 1,410-bp encoding a protein of 469 amino acid residues. The amino acid sequence of the enzyme showed a high degree of identity to those of other aspartases, although these enzymes show different thermostabilities.

We found the occurrence of NAD(P) + -dependent aldehyde dehydrogenase (EC1.2.1.5) in the cells of a psychrophile from Antarctic seawater, Cytophaga sp. KUC-1, and purified to homogeneity. About 50% of the enzyme activity remained even after heating at 50 °C for 65 min and the highest activity was observed in the range of 55–60 °C. The enzyme was thermostable and thermophilic, although it was derived from a psychrophile. The circular dichroism at 222 nm of the enzyme showed a peak at 32 °C. This temperature was closely similar to the transition temperature in the Arrhenius plots. The stereospecificity for the hydride transfer at C4-site of nicotinamide moiety of NADH was pro-R . The gene encoding the enzyme consisted of an open reading frame of 1506-bp encoding a protein of 501 amino acid residues. The significant sequence identity (61%) was found between the Cytophaga and the Pseudomonas aeruginosa enzymes, although their thermostabilities are completely different.

We found the occurrence of valine dehydrogenase in the cell extract of a psychrophilic bacterium, Cytophaga sp. KUC-1, isolated from Antarctic seawater and purified the enzyme to homogeneity. The molecular mass of the enzyme was determined to be approximately 154 kDa by gel filtration and that of the subunit was 43 kDa by SDS/PAGE: the enzyme was a homotetramer. The enzyme required NAD+ as a coenzyme, and catalyzed the oxidative deamination of L-valine, L-isoleucine, L-leucine and the reductive amination of alpha-ketoisovalerate, alpha-ketovalerate, alpha-ketoisocaproate, and alpha-ketocaproate. The reaction proceeds through an iso-ordered bi-bi mechanism. The enzyme was highly susceptible to heat treatment and the half-life at 45 degrees C was estimated to be 2.4 min. The kcat/Km (micro(-1).s(-1)) values for L-valine and NAD+ at 20 degrees C were 27.48 and 421.6, respectively. The enzyme showed pro-S stereospecificity for hydrogen transfer at the C4 position of the nicotinamide moiety of coenzyme. The gene encoding valine dehydrogenase was cloned into Escherichia coli (Novablue), and the primary structure of the enzyme was deduced on the basis of the nucleotide sequence of the gene encoding the enzyme. The enzyme contains 370 amino-acid residues, and is highly homologous with S. coelicolor ValDH (identity, 46.7%) and S. fradiae ValDH (43.1%). Cytophaga sp. KUC-1 ValDH contains much lower numbers of proline and arginine residues than those of other ValDHs. The changes probably lead to an increase in conformational flexibility of the Cytophaga enzyme molecule to enhance the catalytic activity at low temperatures.

集積培養法によって温州ミカンの花から分離株 MK1～3 株を得た。その中で MK3 株は,生理学的試験と 16SrDNA-D1/D2 領域および ITS 領域の塩基配列に基づいた分子系統解析の結果から Saccharomyces cerevisiae と同定された。また Yeastcidin 耐性を有する事から,MK3 株が清酒酵母であることが示唆された。MK3 株は,清酒もろみにおけるアルコール生産量が 17.6%であり,清酒酵母協会 9 号株と同等の発酵力を示した。MK3 株を用いた製成酒は香気成分と有機酸に特徴的な組成を示した。特にMK3株を用いた製成酒は,低いコハク酸濃度,高いリンゴ酸/コハク酸比,高いカプロン酸エチル濃度,高いイソアミルアルコール/イソブチルアルコール比を示した。また,MK3 株は高泡を形成せず,TTC 還元性が Red であることから,清酒製造に実用可能な株であった。MK3 株は,特徴的な風味を形成できる実用酵母として清酒製造での利用が期待される。, The MK3 strain was isolated from Satsuma Mandarin blossom by enriched culture method. On the basis of physiological tests and molecular analyses based on DNA sequences of 26S rDNA-D1/D2 region and ITS region, MK3 was identified as Saccharomyces cerevisiae. Furthermore, it was suggested that MK3 was sake yeast, since MK3 had a tolerance against Yeastcidin. The alcohol productivity of MK3 in sake mash was 17.6%. The MK3 possessed an equipollent fermentative ability in sake mash with sake yeast, kyokai No. 9. The sake produced by MK3 revealed distinguishing composition of aroma compounds and organic acids. In particular, the sake brewed by MK3 showed low succinic acid concentration, high malic acid/succinic acid ratio, high ethyl caproate concentration and high isoamyl alcohol/isobutyl alcohol ratio. The MK3 was a useful yeast for sake production, because it did not form taka-awa in sake mash and it was stained red with TTC. It is expected that the MK3 will be used for sake production as a useful yeast which is able to form characteristic flavor.